This invention relates generally to laser systems, and more particularly, to a laser device which relies upon energy-sharing interactions between atomic trios in gases or active dopants in laser media, and thus forms a new operating principle for continuous-wave solid state lasers.
Lasers which operate with an output wavelength shorter than that of the excitation have been known since the early 1970s. Subsequently, various continuous-wave lasers have been reported in the prior art wherein upconversion occurs by different mechanisms. Moreover, inversions of upconverted energy are reported to have been sustained by avalanche processes, direct pair pumping, and multi-photon absorption with variable contributions from energy transfer. To date, continuous-wave unconversion lasers have operated in Pr, Er, Tm, and Nd-doped solids, exhibiting surprisingly high efficiencies (up to 30%) in simple and robust monolithic designs.
The tremendous growth in laser technology and the actual and potential applications of such devices have placed greater demands on the need for lasers which operate efficiently at short wavelengths. Additionally, the demand has increased dramatically for laser systems which are compact and efficient in their energy utilization. One application which has taken significantly increased prominence in recent years is in the field of data storage technology, particularly in the compact disk medium. There is a need for a new, short wavelength solid state laser which operates in the ultraviolet range, so as to enable smaller focal spot sizes. In the compact laser disk medium, a smaller focal spot size produces a significant increase in the data storage density for a given area.
In the present state of the art, existing compact disk technology relies largely upon GaAs-GaAlAs diode lasers which operate at wavelengths on the order of 800 nm in the near infrared region. A reduction in the wavelength by a factor of two, so as to produce energy in the range of 400 nm, would result in an improvement in storage capacity by a factor of four. Such disproportionate benefit results from the fact that spot radius is proportional to wavelength, but storage density depends on the spot area, which is proportional to the square of the radius. Thus, significant improvements in storage capacity can be achieved from relatively small decreases in operating wavelength. In addition to the foregoing, it is now recognized that the commercial potential of short wavelength lasers is increased by reduction of total power consumption and miniaturization. Of the various categories of conventional lasers which exist, solid state lasers appear to lend themselves best to the achievement of these ends.
There are currently no blue or ultraviolet solid state lasers which operate continuously and which have been developed commercially for compact disk applications or other technologies, such as space communications. There is a need for a new method of laser excitation which permits the development of new short wavelength solid state lasers. There has previously been no suitable excitation mechanism for such lasers.
It is not presently possible to deliver conventional excitation at still shorter wavelengths without severely heating and damaging the solid laser medium. Thus, efforts to produce emission wavelengths short enough to approach the fundamental absorption edge of solids have yielded very low efficiencies. Pump light cannot penetrate to the interior of the laser medium Thus, there is a need for a pumping system which permits excitation at longer wavelengths than either the emission wavelength or the energy of the emitting state with respect to the ground state. In this manner, penetration of the pump light would not be a problem, and deleterious color center formation can be avoided.
It is, therefore, an object of this invention to provide a laser system wherein short-wavelength emission is achieved in response to long-wavelength excitation of laser media.
It is another object of this invention to provide a laser arrangement wherein a population inversion required for light amplification is achieved in response to energy sharing interactions between colliding atoms in gases.
It is also an object of this invention to provide a laser arrangement wherein a population inversion required for light amplification is achieved in response to energy sharing interactions between colliding atoms in active dopants in solid laser media.
It is a further object of this invention to provide a short-wavelength laser system which does not require pump sources with more energy per photon than the emitting state of the laser transition.
It is additionally an object of this invention to provide a laser arrangement which achieves a reduced focal spot size.
It is yet a further object of this invention to provide a laser arrangement which improves the storage density of a compact disk.
It is a still further object of this invention to provide an excitation mechanism for a continuous-wave short-wavelength laser system.
It is also another object of this invention to provide a laser system which can operate at wavelengths on the order of 400 nm.
It is yet an additional object of this invention to provide a laser arrangement which is adaptable for miniaturization, and which is efficient in its energy utilization.
It is still another object of this invention to provide a pair-pumped solid state laser wherein the wavelength of the emitted energy is significantly shorter than that of the pump light.
It is also a further object of this invention to eliminate deleterious color center formation in a laser arrangement.
It is additionally another object of this invention to provide a continuous-wave solid state laser in which pumping is provided by cooperative unconversion due to coupled dopant atoms or ions (pair-pumping or trio-pumping) in the solid laser media.
A still further object of this invention is to provide a laser excitation system in which pump light is absorbed on a strong transition with only one ion of a pair being effectively excited at a time.
An additional object of this invention is to provide a laser system which produces laser light having a wavelength characteristic which is on the order of one-half that of the pump light.